Administration of intravenous fluids to a patient is well known in the art. Typically, a solution such as saline, glucose or electrolyte in a glass or flexible container is fed to a patient's venous access site via a length of flexible plastic tubing such as polyvinyl chloride (PVC) tubing. The rate of flow of the fluid is controlled by a roller clamp which is adjusted to restrict the flow lumen of the tubing until the desired flow rate is obtained.
Flow from the container to the patient may also be regulated by means other than a roller clamp. It is becoming more and more common to use an electronically controlled pump. One type of pump that is used for intravenous fluid administration is a peristaltic-type pump.
Use of peristaltic pumping action is particularly well suited for the medical field. This is because peristaltic pumping action can be applied externally of the tubing carrying the intravenous fluid. This maintains the sterile condition of the intravenous fluid within the tubing while imparting fluid propulsion on the fluid. The peristaltic pumping action can also be applied at any point on the tubing.
In a common type of peristaltic pump used in the medical field, a driving motor is connected to an array of cams angularly spaced from each other. The cams in turn drive cam followers which are connected to corresponding pressure fingers. These elements cooperate to impart a linear wave motion on the pressure fingers. A pressure plate is secured juxtaposed to and spaced from the pressure fingers. The pressure plate holds the tubing against the reciprocating pressure fingers to impart the wave motion on the tubing to propel the fluid.
In a preferred embodiment of peristaltic pumps, the driving motor is a stepping motor which rotates in small increments or steps. While a stepping motor rotating at a high rate of speed gives a visual impression that the rotation is constant, the stepping motor in fact turns through a series of small angular increments or steps which are followed by brief periods of rest. In stepping motors utilized in peristaltic pumps in the medical field, these small angular steps can range from about 0.36.degree. to 7.2.degree. and in a preferred embodiment are about 1.8.degree. . This results in a series of steps of the shaft between 1000 and 50 per revolution or, in the preferred embodiment, about 200 steps per revolution.
The stepping motors utilized in peristaltic pumps effectively drive the peristaltic pumping action. However, the stepping action of the pumps can result in excessive vibration which results in a loud chattering or buzzing noise as a result of amplification by the pump housing.
Various solutions have been proposed to reduce this vibration noise. Traditional shock mounts which consist of four springs connecting the pump housing and the motor frame have been used. These shock mounts, however are designed to absorb and dampen radial vibrations caused by imbalanced forces on the motor shaft and thus do not efficiently dampen the tangential forces generated in the stepping motor.
While "softer" shock absorption can be utilized to eliminate the vibrations and noise, such soft absorption detracts from the accuracy of the stepping motor and presents reliability problems as a result of the soft mounting of the stepping motor to the pump housing.
Another proposed solution is to couple the stepping motor shaft to the cams with a shock absorbing coupler. This solution, however, also suffers from the problem of accuracy and reliability if sufficient absorption is provided to quiet the stepping noise.
What is thus needed is a device which sufficiently absorbs the forces transmitted by the stepping motor to reduce the stepping vibration and noise while maintaining a high degree of accuracy and reliability. The present invention provides such a device.